FIG. 1 depicts a schematic diagram of a wireless local area network in the prior art, which comprises: terminal 101-1, terminal 101-2, and terminal 101-3. Before terminals 101-1, 101-2, and 101-3 can communicate with each other, there must be an agreement between the terminals as to the meaning of the signals that they transmit. For example, the terminals must agree on who talks when, what constitutes a “0” and a “1,” how is an error detected and corrected, etc. In the terminology of telecommunications, this agreement is called a protocol.
The terminals in a local area network share a communications channel such that if two or more of the terminals transmit into the channel simultaneously, a cacophony results and all of the transmissions are corrupted. Therefore, a local area network protocol includes a mechanism for ensuring that only one terminal at a time transmits into the shared-communications channel. This mechanism is known as medium access control. In some implementations, medium access control can provide additional services such as message encryption and authentication, as well as quality of service (QoS) provisioning and power conservation.
FIG. 2 depicts a schematic diagram of wireless terminal 101-i, wherein i is a member of the set {1, 2, 3}, in the prior art. As shown in FIG. 2, wireless terminal 101-i comprises: a host computing device 201 and a wireless station 202, interconnected as shown. Host computing device 201 is a notebook computer, personal digital assistant (PDA), etc. Host computing device 201 sends data to wireless station 202 for transmission to other wireless terminals, and similarly, wireless station 202 receives data from other wireless terminals and sends these data to host computing device 201. Wireless station 202 thus enables host computing device 201 to communicate in wireless fashion with other terminals.
FIG. 3 depicts a conceptual architectural diagram of wireless station 202 in accordance with the prior art. As shown in FIG. 3, wireless station 202 comprises: processor 303, memory 304, higher-layers module 305, logical link control (LLC) 310, medium access control (MAC) 320, physical control 330, transmitter 340, and receiver 350, interconnected as shown.
Processor 303 is a general-purpose processor that is capable of executing instructions stored in memory 304, and of reading data from and writing data into memory 304. Memory 304 is capable of storing programs and data used by processor 303, as is well known in the art, and might be any combination of random-access memory (RAM), flash memory, disk drive, etc. Higher-layers module 305 is capable of executing the tasks associated with the transport, session, presentation, and application layers of the open systems interconnect (OSI) reference model, as is well known in the art.
Logical link control (LLC) 310 performs a variety of tasks, including (i) multiplexing data packets; (ii) sending multiplexed data packets to medium access control 320 via output 311; (iii) receiving packets from medium access control 320 via link 311; (iv) demultiplexing the packets received via input 312; (v) establishing and maintaining logical point-to-point connections over the shared-communications channel; and (vi) provisioning acknowledgements for individual messages on behalf of those network protocols that require such connection-oriented or acknowledged connectionless services, as is well known in the art.
Medium access control 320 performs the channel access function, which ensures that only one terminal at a time can transmit signals onto the shared-communications channel, as well as frame addressing and detection, generating and checking frame check sequences, and delimiting logical link control protocol data units, as is well known in the art. In addition, medium access control may provide additional services including encryption, authentication, and quality-of-service (QoS) provisioning, as well as related, non-communication functions such as power management, as is well known in the art.
Physical control (PHY) 330 administers the physical transmission of signals to other terminals and the physical receipt of signals from other terminals via the network medium (e.g., radio, Ethernet, etc.), as is well known in the art. As shown in FIG. 3, physical control 330 (i) receives data from medium access control 320 via input/output 321; (ii) sends data to transmitter 340 for wireless transmission to other terminals; (iii) receives data from other terminals via receiver 350; and (iv) passes data to medium access control 320 via input/output 321.
Transmitter 340 is a hybrid analog and digital circuit that is capable of receiving data from physical control 330 and of transmitting data wirelessly into a shared-communications channel. Receiver 350 is a hybrid analog and digital circuit that is capable of receiving data wirelessly via a shared-communications channel and relaying data to physical control 330.
As described above, medium access control 320 is theoretically decoupled from the mechanism for controlling the physical (i.e., radio) transmission and receipt of message signals (referred to throughout this specification as the “physical control”). In practice, however, in some wireless local area networks, such as those that conform to the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, the medium access control and the physical control are inextricably intertwined.
In order to mitigate the interdependence between medium access control 320 and physical control 330, U.S. patent application Ser. No. 10/421,265, entitled “Partitioned Medium Access Control,” discloses a medium access control that is bifurcated into (i) an upper medium access control that provides those medium-access-control services that are independent of the physical control, and (ii) a lower medium access control that provides those medium-access-control services that are dependent on the physical control. This is especially advantageous for IEEE 802.11 wireless networks because it enables the standardization, development, and implementation of some of the medium-access-control services to be decoupled from the standardization, development, and implementation of the physical control, while maintaining full compatibility with the installed base of existing IEEE 802.11 equipment. This decoupling can result in the savings of tens or hundreds of millions of dollars to semiconductor, computer, and networking companies.
FIG. 4 depicts a conceptual architectural diagram of the partitioned medium access control disclosed in U.S. patent application Ser. No. 10/421,265. As shown in FIG. 4, medium access control 320 is partitioned into upper medium access control 410 and lower medium access control 420, interconnected as shown. Upper medium access control 410 provides a subset of medium-access-control services that are independent of physical control 330, including transmit queuing, encryption, decryption, authentication, association, re-association, scanning, distribution, and traffic categorization (for the purposes of, for example but without limitation, quality-of-service (QoS) provisioning), as is well known in the art. The upper medium access control may also perform those functions within MAC data service and MAC management service that are independent of physical control 330, including power management, queue management, duplicate detection and filtering, fragmentation, defragmentation, queue management.
Lower medium access control 420 provides remaining medium-access-control services (i.e., those that are dependent on physical control 330), including channel access, receive validation (e.g., frame control sequence, forward error correction, etc.), and those that involve hard real-time functions and/or are physical layer-implementation dependent, such as response control (e.g., clear-to-send [CTS], acknowledgement [ACK], etc.), as are well known in the art.
There are four criteria for determining which functions belong to lower medium access control 420:
i. Functions that are specific to a given physical layer or given type of physical layer;
ii. Functions that require knowledge of the internal state of the physical layer or knowledge of implementation-specific operational characteristics of the physical layer;
iii. Hard real-time functions necessary to generate conformant communication (signaling) sequences as viewed on the (wireless) medium; and
iv. Particular other functions that “belong” in the lower medium access control because of general implementation considerations, or because a party with sufficient clout (e.g., Microsoft, etc.) wants them to be there.